Instructions

Cook penne pasta in boiling salted water per directions on the box. As you are doing this, in a small saucepan melt the butter. Stir in the flour, salt, mustard, pepper and keep on heat until this mixture is smooth. Drain pasta and then stir in the butter mixture either in the pan you cooked the pasta in or a large mixing bowl. Mix well and stir in the milk and the 4 cups of cheese. Pour into a greased tall round (9" x 3 3/4") baking dish or into a 13" x 9" x 2" baking dish. Cover and bake for 50 minutes until bubbly. If you like the top browned, bake uncovered for the last 10 minutes. Once you take it out of the oven, sprinkle the 1 cup mozzarella cheese over the top, let stand for 5 minutes for this to melt and it is ready to serve.